A recent change, motivated by user feedback, was to delay write buffer
flushes as much as possible. Before, littlefs would always flush the
buffer during lfs_file_seek, but now, buffer flushes can be delayed all
the way to lfsr_file_read, or even skipped entirely thanks to bypassing
reads.
This is all fine and dandy, except it's easy to imagine a use case where
a user might really not want a _write_ error to pop out of a _read_
call.
With this new behavior, avoiding this situation is impossible.
So enters a function common to other filesystems: lfsr_file_flush.
However it's value is quite a bit different here. Unlike flush in other
filesystems, this flush does not necessarily make data accessible on
disk. It only writes to the pending file snapshot, which is not
accessible until lfsr_file_sync.
This makes flush a function with a rather narrow scope in littlefs
(pretty much just preventing write errors in read), but since we had
already implemented this function for internal plumbing, it adds _very_
little cost.
I'm more concerned about potential user confusion around sync vs flush.
Curiously, exposing lfsr_file_flush actually _saved_ code size for some
reason. Not sure what would make that happen:
code stack
before: 33544 3072
flush: 33536 (-0.0%) 3072 (+0.0%)
flush+O_FLUSH: 33548 (+0.0%) 3072 (+0.0%)
Christopher Haster
b336e92c66